Efficacy of transvaginal ultrasound-guided twin reduction in the mare by embryonic or fetal stabbing compared with yolk sac or allantoic fluid aspiration.

Transvaginal ultrasound-guided pregnancy reduction (TUGR) is a procedure described for the management of twins post-fixation in the horse. Success rates are often disappointing but are reported to be more favorable for bilaterally situated twins and when intervention takes place before day 35 of gestation. This study aimed to determine whether stabbing the embryo/fetus rather than aspirating conceptus fluids improved the likelihood of success, measured as the birth of a normal live singleton foal. Data from 103 TUGR interventions were analyzed by logistic regression analysis; method of treatment, relative conceptus location (i.e., uni- vs. bilateral), and stage of gestation were included as interdependent factors that potentially influence the outcome. Overall, 34/103 (33%) TUGR interventions resulted in a single live foal. There was no significant difference (P = 0.14) in the outcome between TUGR based on fetal stabbing (12/28: 42.9%) versus fluid aspiration (22/75: 29.3%). There was also no significant influence (P = 0.11) of the conceptuses being located unilaterally (19/65: 29.2%) versus bilaterally (15/38: 39.5%). However, TUGR was numerically more successful (P = 0.05) when performed ≤ Day 35 of gestation (21/53: 39.6%), as opposed to > Day 35 (13/50: 26%). Day 45 may represent an even more critical time point because only 2 out of 15 TUGRs (13.3%) performed beyond this day resulted in the birth of a live foal, compared with 11/35 (31.4%) performed between Days 36 and 45. Although the numbers are low, this suggests that TUGR is not the method of choice for reducing > Day 45 twins. Four pregnancy losses were recorded 1 to 7 months post-TUGR (4/38: 10.5%), and although it is tempting to attribute the losses to TUGR, this rate of late gestation pregnancy loss is normal. We conclude that TUGR by fetal stabbing does not offer significant advantages over fluid aspiration. However, TUGR should be performed before Day 35 of gestation and is considered primarily a salvage procedure to be used when re-breeding is not a viable alternative.
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